Introduction

The measures of central tendency, such as the mean, median and mode, do not reveal the whole picture of the distribution of a data set. Two data sets with the same mean may have completely different spreads. We need a measure that can provide some information about the variation among data values.

The measures that help us to know about the spread of a data set are called the measures of dispersion. The measures of central tendency and dispersion taken together give a better picture of a data set than the measures of central tendency alone. This section discusses four measures of dispersion:

• Range
• Variance
• Standard Deviation
• Coefficient of Valuation